The invention relates to defense systems, and more particularly, to a dual mode seeker/interceptor having integrated IR and laser radar (ladar) capability with a variable FOV.
The flight of a ballistic missile can be divided into three phases: a boost phase, a mid-course phase, and a terminal or theater phase. During the boost phase, which includes the first minutes of flight, reentry vehicles and decoys contained within the launched missile are not released. The mid-course phase is the portion of the flight where the missile is outside the atmosphere as it travels to the target. Reentry vehicles and decoys in the missile are released during this phase, and form what is referred to as a threat cloud. The terminal phase represents the last minutes of flight where the reentry vehicles and decoys reenter the atmosphere on their way to the target.
In typical missile defense systems, the launch of a ballistic missile from anywhere in the world is detected by space-borne assets (e.g., satellites and early warning radars), which will immediately begin transmitting preliminary trajectory information to a mission command center. During the mid-course phase, ground-based radars lock onto the elements in the threat cloud, and provide targeting information for ground-based interceptors with seekers. Near the end of the mid-course phase, these interceptors are launched. Ideally, the seekers discriminate between warheads and decoys in the threat cloud, and destroy the warheads.
Such target discrimination is not trivial, and presents significant technical challenges for hit-to-kill missile defense systems. Each object in a threat cloud must be effectively discriminated from the actual warhead-bearing reentry vehicles. Further complicating this task are the high altitudes (e.g., 50 kilometers or more) at which the discrimination takes place. The bulk of this discrimination task is carried out by the ground-based radars using a number of discrimination techniques, one of which is called stripping, thereby enabling the seekers.
In more detail, stripping relies on atmospheric drag to separate objects based on their ballistic coefficient xcex2=M/CdA, where M is the object mass, Cd is the coefficient of drag, and A is the object area. Stripping is dependent on trajectory and object dynamics (spin and precession). Due to the coarseness of ground-based radar measurements, a significant atmospheric drag is required (altitudes of 50 to 70 km) to produce a measurable amount of relative velocity or separation. At extremely high altitudes (e.g., 100 kilometers or more), such atmospheric drag is substantially reduced or otherwise lacking, thereby impeding early discrimination. The density of objects and the deployment of chaff complicates and delays extraction of target dynamics and subsequent discrimination. In addition, the poor signal quality (e.g., low SNR) can contribute to late discrimination. Early discrimination is desirable for enabling a shoot-look-shoot engagement, appropriate interceptor commitment to threat load, and increased range of destroyed warhead from the targeted or otherwise defended assets.
Using all discrimination means available, the ground-based radar hands over assumed target position information to the seeker/kill vehicle. Typical seekers use a single color, passive IR sensor. Such seekers have less than optimal performance in situations where a potential target is in close proximity to other objects, (e.g., decoys and booster debris), which is typical of a threat cloud. Furthermore, additional error occurs because of the viewing ambiguity associated with a two dimensional (2D) IR seeker. Moreover, the residual effects of prior interceptions, such as the bright light called xe2x80x9cflash,xe2x80x9d limit the effectiveness of the system. In particular, flash temporarily forms an alternate light source, thereby blinding the IR sensor. A laddering effect results, where a next incoming reentry vehicle after an intercept can approach even closer to the defended target due to the flash recovery time required by the interceptor""s IR sensors.
In short, systems employing ground-based radar in conjunction with 2D IR seeker configurations have difficulty discriminating between legitimate targets and clutter, particularly at exo-atmospheric altitudes. Incorrect target discrimination, during high altitude stressing conditions, will substantially reduce the effectiveness of hit-to-kill defensive weapon systems.
What is needed, therefore, is an improved reentry vehicle intercept system that can quickly acquire, discriminate decoys and clutter from target reentry vehicles at very high altitudes, and track the selected vehicle to an intercept.
A reentry vehicle intercept system is disclosed. In one embodiment, the system includes a seeker vehicle configured with an onboard three dimensional (3D) ladar system coordinated with an onboard IR detection system, where both systems utilize a common aperture. The IR and ladar systems cooperate with a ground based reentry vehicle detection/tracking system for defining a primary target area coordinate. The FOV associated with the IR system is focused thereon.
The onboard IR system obtains IR image data in the IR FOV. A variable FOV associated with the ladar system is initially smaller than the IR FOV during engagement, and the ladar system is adapted to systematically interrogate the IR FOV, illuminating possible targets, to discriminate objects located therein. The laser FOV is expandable toward the IR FOV when closing velocity, track angle, or target size subtends the laser FOV. Thus, the laser FOV can expand to any portion of the IR FOV, including a laser FOV that substantially matches the IR FOV.
An onboard processor or processors are programmed or otherwise configured to operate on data obtained on each possible target to perform primary discrimination assessments and other relevant data processing. Such onboard processing enables resolving the possible targets as between decoys/clutter and a reentry vehicle.
For instance, a processing module can be configured to form 3D images of one or more objects included in the field of view based on the detected laser return information. In addition, a processing module can be configured to perform discrimination assessments based on discrimination parameters including at least one of relative velocity, track, and separation data. In addition, a processing module can be configured to perform data fusion between at least two of discrimination assessments, target object map (TOM) data, 3D laser image data, and 2D IR image data.
The ladar system can be configured to operate in various detection modes. For example, the ladar system can be configured to operate as at least one of an angle, angle, range direct detection type system (e.g., Geiger and linear detection modes), and a pulsed Doppler coherent detection type system (e.g., modulated continuous wave radars). In an embodiment where the laser detector includes an array, the ladar system may be configured to operate as a hybrid detection system, where a first portion of the laser detector array performs coherent detection, and second portion of the laser detector array performs linear mode direct detection.
The IR and ladar systems complement each other. The IR provides a broad focus for target acquisition. The narrow focus and pulse capability of the ladar system, with fast 3D processing times, allow higher resolution and the ability to interrogate each potential target within a FOV. The ladar also allows the missile to lock on to an individual target, even in the presence of flash. Robust and reliable threat/decoy discrimination is obtained at high altitudes (e.g., in excess of 100 km).
The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and not to limit the scope of the inventive subject matter.